Where do the excess photons and dileptons in SPS nuclear collisions come from?

Recently the first single photon spectra from CERN energy heavy-ion collisins were reported by WA80, while NA34/3 and NA38 have obtained the spectra for dileptons with the mass up to 4-5 GeV. The production rates for photons and dileptons significantly increase when reactions involving the A₁ meson are included. However, with the conventional expansion scenario, the absolute yields are still significantly smaller than the observed ones. It may indicate that expansion in the "mixed state" takes much more time.